Science gets intoxicated on beauty and conceives conservation. At the San Francisco Botanical Garden, the result is the most important magnolia collection outside China. From now through March the garden is showcasing its "Magnificent Magnolias" with special events, including tours and a magnoliafied mixology class. These "aristocrats of ancient lineage," as legendary plant-hunter Ernest Wilson called them, are celebrated for their spectacular pink and white blossoms, glossy leaves and seductive fragrances: One species is banana-scented.

The garden boasts nearly 100 varieties and species, including nine red-listed by the International Union for the Conservation of Nature. A few are near extinction: Zen's magnolia is down to 18 unprotected individuals on a mountain in China's Jiangsu province. "That makes well-documented collections ever more valuable in the conservation of these trees," curator Don Mahoney said.

In March, assistant curator David Kruse-Pickler will revisit China, the heartland of magnolia diversity. He and Ya-Ling Wang of Fairy Lake Botanical Garden near Hong Kong plan to locate wild populations of sensitive species, record their GPS coordinates and in fall 2014 return to collect seed for propagation.

Magnolias, wrote naturalist Donald Culross Peattie, "have come down to us, by the winding ways of evolution, from an unimaginable antiquity."

Fossilized leaves

Their leaves occur in fossil deposits from the Cretaceous, the era of tyrannosaurus and triceratops. Beetles pollinated them (bees and butterflies did not yet exist) and still do.

The ancient family spread from North America across the Northern Hemisphere during a global hothouse era. Then the magnolias of Europe, Siberia and the American West succumbed to a colder world. In warmer regions of the Appalachians, southern China and the American and Asian tropics, survivors diversified; about 245 species exist today. New forms are still being described.

The garden has some handsome Southern magnolias and a few Central American prizes, but its focus is Asian species. Most were introduced to the West by European collectors in the 19th and early 20th centuries. Some, like Père Armand David (who also discovered the giant panda), were missionaries who botanized on the side. Others worked for botanical gardens, arboretums or commercial nurseries.

Plant-hunting in the Sino-Indian borderlands was no stroll in the park. David and his successors found rough terrain, extreme weather, disease, leeches, suspicious local rulers, rogue generals and bandits.

Risking life and limb

George Forrest survived alone when Tibetan lamas outraged by a British military incursion massacred his party; he hid in the jungle for 10 days, subsisting on a handful of grain.

On a narrow trail along China's Min River gorge, a falling boulder broke Ernest Wilson's right leg in two places. With the leg splinted with a piece of tripod, Wilson had to lie immobilized on the ledge as 50 passing pack mules, with nowhere to detour, tiptoed over him.

Along with danger, they found extraordinary beauty. In his memoir "Plant Hunting on the Edge of the World" (1930), Frank Kingdon-Ward describes Magnolia campbellii: "we see scores of trees, some with glowing pink, others with ivory-white flowers. From our giddy ledge we look down over the wide waves of the forest beating against the cliff, where the magnolia blooms toss like white horses, or lie like a fleet of pink water lilies riding at anchor in a green surf."

Hybridizers' grail

Mahoney calls campbellii one of Strybing's glories: "A 50-foot tree with thousands of large pink flowers held upright against a blue sky is a sight one will remember for the rest of one's lifetime."

Horticulturists played with Asian magnolias as early as 1827, when the saucer magnolia (M. x soulangeana) was developed in Paris. The late Todd Gresham of Santa Cruz created 15,500 hybrids including his "Buxom Nordic Blondes" and "Svelte Brunettes." Nowadays, says Mahoney, most of the hybridizing action is in Britain and New Zealand. The breeders' holy grail: a true yellow magnolia.

Former garden director Eric Walther imported a batch of campbellii seed from Darjeeling, India, in 1934. Most produced typical pink cup-and-saucer blossoms, but one lone tree had white flowers with pendant outer petals. Christened 'Strybing White,' it grew to an estimated 80 feet, the garden's tallest tree.

Younger trees have joined Walther's pioneers, including Asian and neotropical rarities from UC Berkeley's Botanical Garden and Sonoma County's Quarryhill, and one from the Shanghai Botanical Garden via Sen. Dianne Feinstein.

Bay Area hybrids

Grandiflora and the hybrid soulangeana are widely used in the Bay Area. Mahoney suggested alternatives: "Stellata and denudata are both small deciduous trees with fragrant flowers that are easy to grow in our climate and soils. There are many new michelia introductions that thrive in our area; most have wonderful fragrances." Pickler-Kruse is also a michelia fan: "They're great street trees as long as you provide some water."

Magnolia celebration

Highlights of the "Magnificent Magnolias" celebration through mid-March at the San Francisco Botanical Garden, Ninth Avenue and Lincoln Way, Golden Gate Park. www.sfbotanicalgarden.org.

Self-guided tours of the magnolia collection. Download the maps at www.sfbotanicalgarden.org or pick up a copy at the ticket kiosk.